// const reg = new RegExp("a");
const reg = /1/gi;
const str = "asdf123231212gasdasd121";

const newStr = str.replace(/^\d$/g, function (s) {
  return `<${s}>`;
});
console.log(newStr);

// const reg1 = /^\d[a-zA-Z]\d$/
// const reg1 = /\d[a-zA-Z]|[a-zA-Z]\d/;

// 量词
const reg1 = /[a-zA-Z]\d{3}/;
